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All of the commercial two-parts seem fine for calcium and alkalinity, although they might differ in cost. I've used the Kent and ESV magnesium supplements, and they are fine. The SeaChem is mostly magnesium sulfate, so it's not worth getting it, in my opinion. There are DIY recipes that will work, and will save some money, as well.

Personally, I'd stay away from Brightwell, since there seems to be a great deal of high-pressure marketing associated with their products, and at least at one point, it was difficult to get them to publish the ingredients.

A heck of a lot of us simply mix our own from calcium chloride, sodium carbonate/bicarbonate, and magnesium chloride/sulfate. Have you read Randy Holmes Farley's article on DIY two-part dosing? His recipes are pretty much the gold standard of 2-part dosing, and folks like Bulk Reef Supply have made quite a business of supplying the ingredients in convenient packaged proportions.

The DIY 2-part all add NaCl (table salt) over time because the primary ingredients are calcium chloride and sodium bicarbonate. Water changes and dilution are the key to keeping the ionic balance and salinity in the reasonable zone.

The DIY 2-part all add NaCl (table salt) over time because the primary ingredients are calcium chloride and sodium bicarbonate. Water changes and dilution are the key to keeping the ionic balance and salinity in the reasonable zone.

Can you explain why table salt is added. I have been using the DIY 2 part for a couple years, but only when needed to supplement the calcium reactor.

Calcium chloride is CaCl2. Sodium carbonate is Na2CO3 The corals consume the calcium and the carbonate, leaving 2 NaCl for each molecule of calcium carbonate created. Those are the two primary ingredients in the DIY, so that effect dominates the ionic shift.